The present invention relates to a cooling system for an internal combustion engine and to a method of operation thereof, and more particularly relates to such a cooling system and method of operation thereof for a spark ignition internal combustion engine, said cooling system being of a so called double circuit type.
There is a per se well known type of so called double circuit cooling system for an internal combustion engine, in which the cooling jacket in the cylinder head of the engine and the cooling jacket in the cylinder block are interconnected with each other and with a radiator by a conduit system controlled by a system of control valves, and in which, according to selective and appropriate operation of these control valves, the following three types of cooling fluid circuit can be established: (a) when the temperature of the cooling fluid in the block cooling jacket is less than a certain predetermined so called engine warming up temperature value, a so called engine warming up circuit, in which cooling fluid is circulated both through said head cooling jacket and said block cooling jacket (typically in series), but not substantially through said radiator, so that the cooling fluid flows through these two jackets can mix but are not substantially cooled by said radiator; (b) when the temperature of the cooling fluid in said block cooling jacket is greater than said certain predetermined so called engine warming up temperature value but is less than a certain predetermined engine overheating temperature value which is higher than said engine warming up temperature value, a so called separated circulation circuit, in which cooling fluid is circulated around two substantially separate flow paths, one including said head cooling jacket and said radiator, and the other including said block cooling jacket without substantially including said radiator, so that the cooling fluid flows through these two jackets substantially cannot mix; and (c) when the temperature of the cooling fluid in said block cooling jacket is greater than said predetermined engine overheating temperature value, a so called overheat prevention circuit, in which cooling fluid is circulated both through said head cooling jacket and said block cooling jacket (typically in series), and also substantially through said radiator. Such a double circuit cooling system for an internal combustion engine has been proposed, for example, in Japanese Patent Application Ser. No. 55-52025 (1980)(which has been published as Japanese Laying Open Publication Ser. No. 56-148610), Japanese Patent Application Ser. No. 55-68036 (1980) (which has been published as Japanese Laying Open Publication Ser. No. 56-165713), Japanese Patent Application Ser. No. 55-169933 (1980) (which has been published as Japanese Laying Open Publication Ser. No. 57-93620) and Japanese Patent Application Ser. No. 58-90544 (1983), all of which patent applications are assigned to the same assignee as is Japanese Patent Application Ser. No. 221521/83 of which priority is being claimed in the present application.
The effect of the provision of such a double circuit cooling system for an internal combustion engine is as follows. In the case (a) above, in which the temperature of the cooling fluid in the block cooling jacket is less than said engine warming up temperature value, the establishment of the engine warming up circuit in which cooling fluid is circulated both through said head cooling jacket and said block cooling jacket but not substantially through said radiator, with said cooling fluid flows through these two jackets being able to mix but not being substantially cooled by said radiator, means that the temperature rise of the cooling fluid flowing through the block cooling jacket is accelerated, which thus causes the speed of the engine warming up as a whole to be increased as compared with the type of case in which during this engine warming up process the cooling fluid flows in the head cooling jacket and the block cooling jacket are kept separate. Accordingly, the temperature rise of the lubricant in the cylinder block of the engine, which is strongly affected by the temperature of the cooling fluid in said block cooling jacket, is made more quick; and this is beneficial with regard to improving the quality of exhaust emissions of the engine during the warming up operational stage, which in fact is a critical operational stage from the point of view of exhaust emission control. Next, in the case (b) above, in which the temperature of the cooling fluid in said block cooling jacket is greater than said engine warming up temperature value but is less than said engine overheating temperature value, the establishment of the separated circulation circuit in which cooling fluid is circulated around two substantially separate flow paths, one including said head cooling jacket and said radiator and the other including said block cooling jacket without substantially including said radiator, with said cooling fluid flows through these two jackets substantially not being able to mix, means that the cylinder head of the engine is forcibly cooled to a much greater extent at this time than is the cylinder block, which is beneficial with regard to increasing the mechanical octane value of the engine and with regard to avoiding knocking and pinking thereof, and with regard to increasing the performance and the fuel efficiency thereof. Finally, in the case (c) above, in which the temperature of the cooling fluid in said block cooling jacket is greater than said predetermined engine overheating temperature value, the establishment of the overheat prevention circuit in which cooling fluid is circulated both through said head cooling jacket and said block cooling jacket and also substantially through said radiator means that the cooling effect of the radiator is utilized to the maximum possible amount for the engine, thus preventing any overheating. Thereby, by the provision of this double circuit cooling system, the cooling of the internal combustion engine is appropriately performed in all its operational conditions according to the temperature of the cooling fluid thereof, and, without delaying the warming up of the engine, without any risk of occurrence of overheating of the engine, and without deteriorating the quality of the exhaust emissions of the engine, the mechanical octane value is maximized, thus providing good performance and fuel economy.
Such a cooling system, and such a method of operation thereof, are beneficial, but certain questions and problems remain to be resolved. In particular, in such a cooling system, typically a cooling fan or fans are also used to blow air at the radiator. Such a cooling fan system may either be powered from the crankshaft of the engine, optionally via some form of clutching device, or electrically by an electric motor. In either of these cases, since actually such a cooling fan system is not required to blow air at the radiator during all operational circumstances (for example, when no cooling fluid is being passed through the radiator, no draft therefor is required), if the cooling fan system is in fact being powered at all times, power is wasted: either mechanical power in the case that the fan system is mechanically powered from the engine crankshaft, or electrical power in the case that the fan system is electrically powered. Further, there is a risk that in some circumstances the engine may be overcooled.
In principle, the cooling fan system of such an engine should be operated (during the engine warmed up state) only when the temperature of the cooling fluid circulating through the cooling jacket of the cylinder head of the engine is higher than a certain fan system trigger temperature value. This fan system trigger temperature value should be set substantially less than said engine warmup completion temperature in order to keep the cylinder head of the engine at a much lower temperature than the cylinder block as explained above. Now, if it were conceived of to control the cooling fan system only according to the temperature of the cooling fluid circulating through the cooling jacket of the cylinder block of the engine, the problem arises that the cooling fan system might be unnecessarily operated once the block cooling fluid temperature reached its reference trigger value, even though the head cooling fluid temperature was not properly high; or in an extreme case even while the engine warming up circuit was being provided. Further, in the case that the cooling fluid circulating through the cooling jacket of the cylinder block of the engine is partially diverted for supplying heat to a heater core of a heater for the passenger compartment of the vehicle incorporating the internal combustion engine, which is typically the case, it may occur during cold or winter exterior weather conditions that, when the engine is idling or running under light load and the separated circulation circuit of case (b) above is being provided by the cooling system, only by the operation of the passenger compartment heater, enough heat is removed from the cylinder block cooling fluid circuit of the engine to cause the temperature of the cooling fluid in said block cooling jacket to drop below said engine warming up temperature value, so that the engine warming up circuit of case (a) described above comes to be provided. When this happens, the temperature of the cooling fluid in said block cooling jacket temporarily abruptly rises, due to the sudden mixing of the cooling fluid in said block cooling jacket therewith; and, if the cooling fan system were controlled as suggested above only according to the temperature of the cooling fluid circulating through the cooling jacket of the cylinder block of the engine, then at this time point said cooling fan system could very likely be operated unnecessarily, which would be disadvantageous and would impair the operation of the passenger compartment heater, as well as perhaps overcooling the engine.